The Pentagon's order to deploy large numbers of combat troops, warplanes and a hospital ship in the Gulf have created a near unstoppable momentum towards war with Iraq, US military analysts said yesterday.

Over the year, the US military has conducted low-profile preparations for a conflict, moving headquarters and equipment into the region. But the new deployment orders reported over the weekend represent a serious commitment of manpower and resources from which it will be hard to climb down without ousting Saddam or at least forcing his disarmament.

"There is a bit of 1914 in this in that once mobilisation begins, it's hard to turn it off. There are financial costs and practical costs," Ralph Peters, a former army intelligence specialist on the Middle East said. "You've already decided to take the political costs mobilising reserves, and the world is psychologically prepared for it. It would take an act of great fortitude to stop the train now."

The White House wanted to hold back the deployment orders until after the new year, but the Pentagon (which would have preferred the large-scale troop build-up to begin in early December) insisted it begin earlier if an invasion was to take place before March. The Iraqi spring heat begins to make desert warfare much more difficult.

After the defence secretary, Donald Rumsfeld, signed the deployment order, the army's 3rd Infantry Division based in Georgia was put on alert. The 101st Airborne Division and the 1st Marine Expeditionary Force, which have both been intensively rehearsing urban warfare techniques, are also preparing to leave for the Gulf.

About 25,000 troops are expected to fly to the region in the next few months to join 60,000 already there, with many more on 96-hour notice to leave. Up to 80,000 soldiers are expected to spearhead an assault along with marines and airborne troops.

The air force's Air Combat Command sent out deployment orders to F-16 and F-15 fighter units in Virginia and North Carolina and B-1 bombers based in North Carolina. The navy put the 10,000 sailors on board the George Washington aircraft carrier and its battle group of warships and submarines on 96-hour alert, despite the fact that they had just returned from a six-month tour of duty. And in a move that some military experts had earlier predicted would be a signal that the administration was serious about going to war early in 2003, a hospital ship, the USS Comfort was ordered to prepare a 1,000-bed trauma centre and make preparations to leave for Diego Garcia in the Indian Ocean.

The Bush administration insists that no decision has yet been taken on whether to go to war, while it waits for results of UN weapons inspections under way in Iraq. But most observers believe that only a radical move by Baghdad - such as a confession to stockpiling weapons of mass destruction - or a dramatic worsening of the North Korean crisis can stop an invasion.

"Nothing is inevitable, but the logic of the situation points towards a war sometime in February," said Gary Schmitt, the head of Project for a New American Century, a conservative thinktank with close links to the administration.

"It's very hard for a country to mobilise for war, and not to go for war without a very serious reason. If you signal to the world that you're serious, and you don't do anything, then you're saying you're not a serious country."

Mr Peters said that the international community now believed that a conflict was inevitable and that regional allies like Saudi Arabia were prepared to offer limited assistance, after much cajoling by US officials.

Stephen Baker, a retired US Navy rear-admiral now at the Centre for Defence Information, said that the troops on standby would be able to fly in to the Gulf and pick up their pre-positioned equipment in a few days.